Catalytic converters were first used in the early 1970s to reduce harmful exhaust emissions, such as carbon monoxide, hydrocarbons and nitrous oxides (NOx) produced by automobiles. These converters are still employed and are typically made by forming a honeycomb support structure comprised of metal or ceramic (e.g., cordierite) covered by a coating containing a precious metal catalyst. The catalyst-coated structure is placed in a metal container connected to the exhaust system, such that the exhaust gas flows through the channels of the honeycomb.
The catalyst coating is typically applied using a wash coat consisting of nanometer size particles of precious metal (e.g., platinum, palladium and rhodium) deposited on micrometer size agglomerated particles of alumina. The coating thickness is typically about 10 to 100 micrometers thick covering the entire surface of the metal or cordierite, including any surface roughness. The catalyst coating is made this thick to provide sufficient catalyst loading within the volumetric limitations of the converter device to ensure adequate initial performance and an adequate performance life of the catalytic converter.
Even though these catalytic converters are effective in reducing emissions once they reach operating temperatures, they are not very effective at reducing emissions upon “cold start.” Cold start is when the catalyst temperature is low (e.g., ambient) and the rate of catalytic reaction is too slow for effective treatment of exhaust gas. As the hot engine gases heat the catalyst, a temperature where the catalysts start to operate (generally referred to as light-off) is reached and reactions occur causing, for example, the oxidation of CO to CO2. As a result, it is well recognized that automobiles are the most polluting during the first minutes after they are started.
Considering the amount of automobiles and ever more stringent clean air standards, this initial start-up pollution has become more of a problem. To solve this problem, several approaches have been tried, such as the preheating of the catalytic converter using resistance heating powered by the auto's battery. This approach suffers from excessive wear on the battery, added complexity and inability to start the vehicle and go immediately (i.e., it takes a couple of minutes for the converter to warm up). Another approach has been the capture of heat of the engine, which can be used sometime later to heat the converter. This approach also suffers from added complexity, the inability to start and go immediately and limited time where the heat may be retained (e.g., 24 hours or less).
Accordingly, it would be desirable to provide a catalytic device and method of forming said device that overcomes one or more of the problems of the prior art, such as one of those described above.